The Chenyulan river basin, located in central Taiwan, is characterized by frequent landslides and debris flows. The catastrophic hazards, especially that induced by typhoon Herb in 1996, have drawn great concerns islandwide. It is believed that a better understanding on the spatial and temporal distribution of these rapid geomorphic changes (i.e., landslides and debris flows) over longer time span will be very helpful on risk assessment and hazard mitigation in this region. The method applied was to make a thorough examination of 17~29 versions of aerial photographs (ranging from 1951 to 2000) of four selected small catchments located in the northern part of the Chenyulan basin (i.e., Tzuzaichiao, Shanganchiao, Peiputzai, and Fengchiu catchment). According to the frequency of landslides and debris flows which identified from available photographs over last 50 years, the Shanganchiao catchment is the least responsive to external inducing events among four catchments, while the Fengchiu catchment is the most, which has experienced six debris flow events over the period.